23 August 2012

Ragone plot showing the energy density and power density of photothermally reduced graphene. For comparison, activated carbon control has also been plotted. Although activated
carbon lies well within the Li-ion battery region for lower C rates (1 C), its performance drastically reduces at higher
power rates. Credit: ACS, Mukherjee et al. Click to enlarge.

Researchers at Rensselaer Polytechnic Institute led by Nikhil Koratkar reported the use of photoflash- and laser-reduced free-standing graphene papers as high-rate capable anodes for lithium-ion batteries in a paper published in the journal ACS Nano.

Photothermal reduction of graphene oxide—by photoflash or laser—results in an expanded structure with micrometer-scale pores, cracks, and intersheet voids. This open-pore structure enables access to the underlying sheets of graphene for lithium ions and facilitates efficient intercalation kinetics even at ultrafast charge/discharge rates of >100 C, they reported. The photothermally reduced graphene anodes are also structurally robust and display outstanding stability and cycling ability. At charge/discharge rates of 40 C, the anodes delivered a steady capacity of 156 mAh/ganode continuously over 1,000 charge/discharge cycles, providing a stable power density of 10 kW/kganode.

In addition, the team suggests that such electrodes could be mass scalable with relatively simple and low-cost fabrication procedures, thereby providing a clear pathway toward commercialization.

Although standard Li-ion batteries can provide very high energy densities, they are unable to provide high power densities, the authors note. A lithium-ion battery provides capacities through lithium intercalation with an active electrode material; its high-rate performance is thus
largely governed by Li+ diffusivity and electron conductivity.

It should be noted that achieving high capacities at
elevated C rates is particularly challenging since the
time available for lithium ions to diffuse through the
anode and intercalate is now significantly shorter. As a
result, only a partial lithiation is achieved, if at all, and
the capacities are often very low. Another limitation
with ultrahigh charge/discharge rates is the electron
transfer mechanism. The electron conductivity of the
anode material directly influences the charge transfer
mechanism and thus largely governs the achievable C
rates. Finally, a high surface area is desirable for
operating at high rates since it is of prime importance
that the lithium ions have sufficient active sites for
intercalation to make up for the diffusivity constraints.

...Here we describe the photothermal reduction of
free-standing graphene oxide paper to obtain graphene anodes with a unique “open-pore” structure. The energy from a camera flash or laser causes instantaneous and extensive heating of graphene oxide and
induces a deoxygenation reaction. We show that
this rapid outgassing creates microscale pores, cracks,
and voids in graphene paper, which enhances lithium
intercalation kinetics at ultrafast charge/discharge
rates. We attribute this to better ion diffusivity, greater
access to the underlying graphene sheets through the
micropores, and improved electrolyte wetting of the
electrode.

—Mukherjee et al.

They found a stable capacity at 5 C of
of ∼370 mAh/g, which is the highest capacity reported
at 5 C for a pure carbon anode (without any additives)
in a Li-ion cell. The capacity drops with increasing C
rate, but the electrode is still capable of delivering ∼156 mAh/g at 40 C and ∼100 mAh/g at
100 C.

...these are by far the highest
capacities reported so far for pure carbon-based anodes (without additives) at 40 and 100 C and are an order of magnitude higher than conventional graphitic
anodes. Most importantly, these capacities were highly
stable and could be maintained for over a thousand
cycles of continuous high-rate charge/discharge. While
laser-scribed graphene has recently been demonstrated in an electrochemical capacitor, to our knowledge, this is the first demonstration of photoreduced
graphene electrodes in lithium-ion batteries.

—Mukherjee et al.

Along with Koratkar, co-authors of the paper are Rensselaer graduate students Rahul Mukherjee, Abhay Varghese Thomas, and Ajay Krishnamurthy, all of the Department of Mechanical, Aerospace, and Nuclear Engineering (MANE).

The study was funded by the National Science Foundation, and supported by Koratkar’s John A. Clark and Edward T.Crossan Endowed Chair Professorship at Rensselaer.

Koratkar is a professor in MANE and the Department of Materials Science and Engineering at Rensselaer. He is also a faculty member of the university’s Center for Future Energy Systems and the Rensselaer Nanotechnology Center.

That depends. How will I, as the researcher, get paid for this. Is everything (IP I create) owned by my employer? If so, supply me, please, with motivation. Oh, you'll let me keep my job. Why, how considerate. How will you know that I am trying to actually solve the problem? I see MBAs as managers that can't make a technical determination. I'll just say the ten magic mumbo jumbo words, nod at the marketing director and say "That's a really good idea, sir", and they'll all get a warm and fuzzy feeling. Thus I stretch out my career and never really give up what has value. If I solve the problem in six months it could be determined that they no longer need me. And what have I done? Made the MBAs successful and gotten myself unemployed. It's not a simple process to change the carbon in a batteries, this will take years of effort and product testing. I think we actually need to step back and try and understand the basics. We don't really have a good fundamental understanding of the phenomena.

Did B4 just confirmed that R & D + mass production will continue to move (at an accelerated rate) to countries with different work ethics, higher morality and better attitude. Those countries may very be China, South Korea, Japan, India, etc?

When developed, this technology may very well produce the improved very quick charge/discharge batteries required for extended range BEVs. Their very quick charge/discharge capabilities will also make them very good candidates for improved HEVs and PHEVs.

This is why a small company needs to be spun off from RPI with the license to do this research and the geeks need to have some share in the company ownership, even if small.
One percent of a small company that grows to a multi-billion doller jackpot still makes the geeks happy.
:-)

" I think we actually need to step back and try and understand the basics. We don't really have a good fundamental understanding of the phenomena."

PLEASE, 150 years since the first 3 component, no moving parts, storage battery and we still don't know how to replace one of the three components - even if it's part of a decades commercialized lithium-ion battery - without years of per-commercialization?

BOTE here: at 100 mAh/g at 100C, the anode is good for about 10 kA/kg or ~36 kW/kg. If you can get about the same out of the cathode, and the cathode and anode comprise 50% of the weight of the cell, you get 9 kW/kg net.

11 kg of battery would yield roughly 100 kW of peak power, though storing just 1 kWh. That's enough for some pretty impressive hybrid performance in dynamic braking and acceleration; it would totally transform the auto industry.

Yes, the $$$$$B in public money given for R % D often ends up in the hands of the 1% to 3% to further increase their wealth. It is ridiculous to use borrowed $$$B or $$$B from the 97% to further enrich the 1% to 3%.

There must be better ways to do it and/or to equally enrich the 97%? How can the 97% collectively get a good return on their investments/taxes.

Couldn't governments loan seed $$$$ at a fair interest rate and get convertible preferred shares instead of giving away $1T/year in subsidies, grants, tax breaks, tax credits, hand outs etc? Why governments could not become investors like pension funds and make money at the same time?

The $1T/year saved could repay the national debt in less than 20 years.

It all seems to make so much sense but who would pay (black and/or white $$$$) for elections? A new law would be needed to limit election expenditures to a total of $10 per elector or vote or so. Treasury could pay most of it. Very low (under $100) individual contributions could be tolerated but the $10/voter expenditures limit should be respected/imposed.

Something has to change. Otherwise, our democracy style will keep on deteriorating and inequalities will keep growing. The 1% will have an absolute control on politics, laws, economy, education, health care, justice and the general well and not so well being of the nation. We will be back to the 12th century's Lords and Kings with absolute powers. We are getting there at an accelerated rate.

aser—results in an expanded structure with micrometer-scale pores, cracks, and intersheet voids. This open-pore structure enables access to the underlying sheets of graphene for lithium ions and facilitates efficient user